1. Field of the Invention
This invention relates to a printed wiring board having a rigid substrate as a core material, and on at least one surface of which is layered a flexible substrate, and to a manufacturing method for the printed wiring board.
2. Description of Related Art
Among the printed wiring boards, known so far, there are a so-called rigid substrate, carrying a tough core material, formed e.g., of a glass epoxy resin, with the core material carrying a wiring pattern, and a so-called flexible substrate, having a flexible core material carrying a wiring pattern.
Meanwhile, in a portable high-performance electronic equipment, such as a digital mobile equipment, in which a demand is raised for increasing the transmission rate and the memory capacity, there is also raised a demand for reducing the size and weight of the equipment in order to improve its portability. In keeping up with this demand, it is required of the printed wiring board to increase the number of I/O pins and to reduce the weight of semiconductor.
Among the aforementioned printed wiring boards, there is a multi-layered printed wiring board having plural substrates layered together and plural electrically conductive layers.
However, in a multi-layered rigid substrate, a through-hole needs to be bored in each substrate for establishing electrical connection across the respective conductive layers. If this through-hole is formed, the conductive layer provided on the core material and the inner wall surface of the through-hole need to be plated. For this reason, in a multi-layered rigid substrate, the copper foils, forming the respective conductive layers, cannot be reduced in thickness, so that difficulties are encountered in further reducing the thickness and weight of the entire substrate or in forming fine patterns thereon. Moreover, in the multi-layered rigid substrate, a wiring pattern is formed on each surface of the core material, a further core material is bonded on each surface of the core material, now carrying the wiring pattern, and a wiring pattern is formed on the so-bonded core materials. Thus, if malfunctions occur in the course of the manufacturing process, the substrates bonded previously need to be discarded in their entirety, thus decreasing the yield to render it difficult to improve the production efficiency or to reduce the production cost.